In many industrial applications it is necessary to remove or dissolve salt deposits (scale) from surfaces. In oil-well stimulation processes it is sometimes necessary to dissolve a portion of the hydrocarbon-bearing rock formation. In some cases it may be necessary to dissolve scale on wellbore surfaces or in the formation, and a portion of the formation as well. In many cases it may be desirable to remove or dissolve as much material as possible with as limited an amount of treatment fluid (or treating composition) as possible. In many cases, the salt and/or formation may be difficult to dissolve. In many cases the salt and/or formation may be coated or at least partially coated with oil. When such oil might interfere with the process, the treatment fluid used to dissolve the salt and/or formation usually includes a mutual solvent. This is a component that is soluble in the treatment fluid but also miscible with the oil so that it causes the oil to be miscible with the treatment fluid and allows good contact of the dissolving component(s) of the treatment fluid with the salt and/or formation. The mutual solvent promotes water-wetting of surfaces such as minerals and metals and at least partial removal of hydrophobic materials such as oil-based muds, oils, paraffins and asphaltenes from the surface. This in turn promotes interaction of other components of the treatment fluid with the surface.
Substantially aqueous compositions are generally used to carry out these operations. Such compositions are usually made up of an acid, a chelating agent for the cation in the scale or formation, or both. When it is desirable to limit the volume of treatment fluid used and/or when the salt or formation is only sparingly soluble in the fluid, very high concentrations of acid and/or chelating agent are needed. Typical mutual solvents are multifunctional nonionic materials such as alcohols, glycols and glycol ethers, nonionic surfactants, and the like. Mutual solvents commonly used in industrial cleaners and oilfield treatments cannot form stable one-phase fluids in these treatment fluids that have very high concentrations of electrolytes.
There is a need for mutual solvents that form stable one-phase fluids in aqueous compositions containing very high electrolyte concentrations.